The flowers of common dayflower are truly blue, and they have only two conspicuous petals. A fast-growing, sprawling, but shallow-rooted weed, this introduced species commonly annoys gardeners.
Common dayflower is an herbaceous annual plant that sprawls along the ground like a vine, often rooting at the nodes.
The flowers last for only a day, emerging from a boatlike sheath, one at a time. There are 3 petals: 2 large blue petals above, plus 1 much smaller, white or greenish-white petal below. There are 6 stamens: 3 on short stems, which are sterile (these are called staminodes), and 3 on longer stems, which produce pollen.
Blooms May–October.
The leaves are alternate, clasping the stem, narrowly ovate to lance-shaped. The sheaths at the base of the leaves are ⅜ to ¾ long.
Similar species: There are 4 more dayflowers in the genus Commelina recorded in Missouri. They have similar characteristics.
- White mouth, or slender dayflower (Commelina erecta), is common south of the Missouri River and scattered in the northern part of the state; it grows on stream banks, sandbars, gravel bars, rich bottomland and upland forests, glades, bluff ledges, and disturbed sand prairie; also along sandy roadsides and in fallow fields. Like common dayflower, the smaller, lower petal is white, but unlike common dayflower, the margins of the boatlike sheath at the base of the flower are fused (not open) in its basal third.
- Climbing, or spreading dayflower (Commelina diffusa) is scattered nearly statewide, most commonly in the southern counties, and occurs on mudflats and gravel bars along rivers and streams, margins of lakes and ponds, other disturbed land along streamways, and bottomland forests, also in cultivated fields and untended lawns. Unlike common dayflower (C. communis), all three petals are blue, and the leaf sheaths are no longer than ⅜ inch.
- Virginia dayflower (Commelina virginica) is scattered south of the Missouri River and occurs in bottomland forests, stream banks, edges of swamps and sloughs, and ditches. All 3 petals are blue and conspicuous. Interestingly, it is the only dayflower in the state that grows from rhizomes. It is the most robust of the state's dayflowers and is common along ditches in the Bootheel, but grows throughout the Ozarks, too.
- Carolina dayflower (Commelina caroliniana) is native to India and is not native to Missouri; in our state it is known only from a few historical collections in Jackson County. It is very similar to C. diffusa. (It was named from specimens collected in the southeastern United States before botanists realized the species had been introduced there, in Charleston, probably as a contaminant in rice shipments.)
Height: 1–2 feet. The sprawling, branching stems can reach nearly 3 feet long.
Statewide.
Habitat and Conservation
Occurs in disturbed soils near waterways, ditches, low woods, bottomlands, waste places, cultivated fields, gardens, near dwellings, and moist roadsides and railroad embankments.
This species of dayflower is native to eastern Asia and has been introduced nearly worldwide. Where it is not native, it is often considered a weed.
Status
Nonnative, introduced plant. Native to East Asia and northern parts of Southeast Asia. Often considered a weed.
Human Connections
A fast-growing but shallow-rooted weed that annoys gardeners, but a few people cultivate it as an ornamental.
Researchers have found that this species can absorb and retain metal-containing compounds, so this plant can possibly be used for revegetating and removing pollutants from copper mines.
In Asia, it is cooked and eaten as a green vegetable and as a medicinal herb.
In the 18th and 19th centuries, blue pigment from the flowers of this plant was used to color many of Japan’s famous woodblock prints. Because the blue color rapidly faded to a greenish yellow, the artists switched to more stable pigments, particularly the synthetic Prussian blue, when it became available. (The famous Hokusai print The Great Wave Off Kanagawa used Prussian blue.)
The genus name Commelina honors two prominent Dutch botanists, Jan Commelin (1629–1692) and his nephew Caspar Commelin (1636–1693); they are represented by the two showy blue petals. A third member of the Commelin family died before making a name in botany; the smaller, white petal thus represents the deceased Commelin.
Ecosystem Connections
Bees and other insects visit the flowers, which lack nectar; they are attracted in part by the showy yellow, though sterile, staminodes.
Other insects eat the foliage, which deer and other mammals relish as well.
Dayflowers and spiderworts are in the same family. Most of the approximately 700 species in the Commelinaceae are tropical or subtropical. You are probably familiar with houseplants called inch plants (Tradescantia) that have all-purple or purple-striped leaves, juicy stems, and a sprawling habit similar to dayflower. The flowers of inch plants have three equal petals, though, and they’re in the same genus as spiderworts.
